Enveloped RNA viruses such as the myxo-, paamyxo-, toga- and rhabdoviruses provide good models for the study of membrane structure and biogenesis. In addition, these viruses are similar in many ways to the oncornaviruses, including overall virion structure and mode of release of the enveloped virions by budding through the host cell plasma membrane. These similarities are underscored by the successful formation of interspecies hybrid virions between oncornviruses and vesicular stomatitis virus. Therefore, it is also likely that the lytic enveloped RNA viruses are useful models for an understanding growth and assembly of the oncornaviruses. Intracellular events leading to the release of mature virions have been described in detail for several enveloped RNA viruses. The aim of this proposal is to develop in vitro approaches to help elucidate the molecular mechanisms involved in assembly of enveloped RNA viruses. Specifically, we plan to develop techniques for the dissociation and reassembly of enveloped RNA viruses, to study interaction between purified viral components from wild-type and temperature-sensitive mutants blocked in virion assembly using biochemical and physicochemical techniques, and to attempt in vitro phenotypic mixing experiments using envelope components from oncornaviruses to further elucidate the molecular specificities involved in the assembly process.